The best observation yet of the energy-time entanglement of photon pairs has been made by physicists in Canada. The feat was possible because Jean-Philippe MacLean, John Donohue and Kevin Resch of the University of Waterloo could measure the arrival times of photons to sub-picosecond precision.

Entanglement is a result of quantum mechanics that allows the properties of two or more photons (or other tiny particles) to be correlated more strongly than allowed by classical physics. Once seen as a quirky aspect of the quantum world, entanglement is now being used to create practical systems for quantum cryptography and quantum communications.